The present invention relates to a diagnosis system for internal combustion engines, and more particularly to a system for diagnosing failure of a starter operation sensor of an engine mounted on a motor vehicle.
An electronic fuel-injection system of the type which is provided with a computer operable to compute various factors, such as starter operation, throttle position, volume of intake airflow, intake manifold vacuum and coolant temperature in order to produce output signals for driving solenoid-operated injection valves is known. The starter operation sensor is provided to produce a starter signal, when a starter for the engine is operated. With a cooled engine, air-fuel mixture is enriched by the starter signal. If trouble occurs in the starter operation sensor system, the starter signal is not applied to the computer. Consequently, lean air-fuel mixture is supplied to the engine, which causes difficulty in the starting of the engine. On the other hand, if the starter signal supply continues after starting the engine, the mixture is extremely enriched, which decreases the driveability of the vehicle and further will stall the engine.